This invention relates to control of phased array systems generally, and more particularly to distribution of data to the individual element modules for controlling the phase shifters.
The prior art in respect to phased array antennas and the technique for generating the required multi-phase excitation signals in controllable fashion, are extensively described in the technical literature. The text "Radar Handbook" by Merrill I. Skolnik, (McGraw Hill 1970) provides considerable insight and background information in respect to the design of phased array systems.
In general, a phased array, which provides maximum scanning flexibility and random, inertialess, beampointing capability, involves the individual excitation of the radiating elements of the arrays, or at least individual rows or columns of elements treated discretely in respect to the phase of the RF excitation thereof. In some of the most advanced and most flexible phased array systems, two-dimensional arrays, such as planar arrays, are used which require individual excitation of all of the elements in order to provide a pencil-beam with pointing flexibility desired throughout a solid angle of coverage.
What may be referred to as the classical approach to the problem involves the use of controllable individual radio frequency phase shifters between the source of transmittable RF, and each of the aforementioned array radiating elements (antenna elements). Chapter 12 of the aforementioned Radar Handbook reference describes known types of controllable phase shifters available for the purpose. These include the so-called ferrite phase shifters, and those employing semiconductor diodes. The former can provide either stepped or continuously variable phase shift within recognized limits in response to a digital or analog type control signal, whereas the latter generally provide phase shift in discrete steps (usually digitally controlled). The manner of digital or analog control is explained in the text aforementioned.
U.S. Pat. No. 4,028,702 to A. M. Levine describes a phased array system using fiber optic delay lines to provide the actual phase shift devices, using light energy modulated by an RF signal. The use of fiber optic lines for communications, including transmission of digital data, is well known. Examples of fiber optic transmission links are shown, for example in U.S. Pat. Nos. 4,052,611; 4,135,202; 4,160,157 and 4,201,909. A text "Fiber Optics" by Edward A. Lacy, 1982, describes components and systems of fiber optics for communications.
Phased array antennas can be electronically steered by controlling the phase of the RF signal at each transmit/receive element. Conventionally a digitally controlled phase shifter at each element implements this phase control. It is customary for the radiating elements to be laid out with a regular spacing on a two-dimensional surface, for example a uniform rectangular grid in the XY plane, comprising rows and columns of radiators. As is well known, the antenna beam can be steered in one direction by applying a relative phase shift between rows and in an orthogonal dimension by applying a relative phase shift between columns. At the element, the row (Y) and column (X) phase change commands are added to give a single control to the phase shifter.
The magnitude of the problem of distributing the data can be appreciated when the requirements of modern agile beam antennas are considered. It is not unusual to have 100 rows and 100 columns, with an 8-bit command word to be communicated in one microsecond. The need to remove an element for maintenance means that four connectors (X, Y, male, female) are required at each of 10,000 elements. Access to the elements of the array is further complicated by the requirement to distribute other services such as RF power for transmission, RF signal on reception, DC power for logic etc., and possibly a cooling medium.
In addition to communicating data in the form of a multiple bit word, synchronization data in the form of a timing pulse precise to a few nanoseconds, is required in a specialized application of agile beam radars. It is usually required that the delay times in the distribution paths of this pulse be equal to all receptors.